The present invention relates to an ignition system for an internal combustion engine, and particularly to an ignition system comprising a primary current control switch provided in parallel with an exciter coil and the primary of an ignition coil energized by an exciter coil producing an AC voltage in time with the rotation of the engine crankshaft, the primary current control switch being made conductive in advance of the ignition angle and made nonconductive at the ignition angle to cause sudden increase in the primary current.
Ignition systems of this type rely on a principle wherein the primary current variation is accompanied by the variation in the magnetic flux in the core of the ignition coil and the larger magnetic flux variation results in the higher secondary voltage and the larger spark energy. In certain applications, the primary current variation is insufficient, and hence the magnetic flux variation is insufficient, and accordingly the magnitude of the secondary voltage and the magnitude of the spark energy are insufficient.